This invention relates to the separation of one or more constituents of blood, and is more particularly directed to a closed system employing centrifugal force for separating different constituents from whole blood based on density or size, such as the separation of platelets and plasma from whole blood, and to the method for carrying out such separation.
Whole blood consists broadly speaking of red blood cells, white blood cells, platelets and plasma. Hemapheresis, which is directed to the separation of one or more constituents of blood, encompasses the extraction of many different constituents in the present state of the art. Plasma, for example, is separated from whole blood taken from donors and stored, with the packed cell remainders from the blood being returned to the donors. Red blood cells are concentrated and stored or reused, sometimes being held in frozen state before reuse.
There are numerous therapeutic apheresis applications under study in which, using temporary or permanent separation of blood constituents, treatments or procedures are applied with sometimes dramatic benefit in amelioration of specific diseases or afflictions. It is sometimes desirable to separate leukocytes (white cells) from the red blood cells. In other instances it is sought to extract platelets, which have a principal role in the clotting function, from red blood cells, with or without plasma. In all of these applications, the fragile blood tissue must be handled in a non-traumatic manner to avoid the introduction of hemolysis or the initiation of the clotting action.
Hemapheresis has heretofore principally been carried out using centrifugation techniques, or membrane filtration systems. Spinning whole blood in a centrifuge at an appropriately high rate separates constituents in accordance with their density, and by using a sufficiently high rate and an adequately long period of time a fine discrimination in constituents, in accordance with density, can be achieved. Batch centrifugation, however, is cumbersome and lengthy and not suitable for many applications in which it is desired to extract more than one constituent or return packed cells or other constituents to a honor.
Accordingly, cell separators have been developed and are in use, such as the Model 30 offered by Haemonetics Corp. for cell extraction. This includes a disposable unit comprising a rotatable rotor with an interior core so configured that heavier matter moves to the outside diameter of the rotor/core combination, causing lighter matter to pass through interior ports to an outlet. To achieve appropriate centrifugation forces so as to separate materials that are quite close in density requires high speed operation, and this device must be run for a substantial period of time before separation occurs. The Haemonetics unit accordingly is driven at approximately 4800 rpm and is quite expensive (in the range of $45.00 per unit) for a disposable device. The great majority of such hemapheresis units are disposables that are used only once, because of the likelihood of transmission of infectious agents from one donor to another.
Furthermore the Haemonetics device is regarded as an open path configuration, in that the inlet and outlet paths for the constituents can communicate with the exterior environment through rotary seals. Microbe infiltration is a danger with such open systems, in consequence of which the FDA requires that the extracted matter be used within 24 hours to avoid the possibility of contamination.
Membrane filtration using a spinning rotor within a concentric shell has now been shown to be extremely effective for separating some constituents of blood from others, as for example separation of plasma from leukocytes, platelets and red blood cells. There is a substantial difference in density and in the size of the elemental plasma which passes through the membrane relative to the cellular matter which is not filtered. However, when it is desired to separate certain cellular matter from other cellular matter, sizes may vary but little, as in the case with platelets which are of only slightly lower density in comparison to red blood cells. Membrane filtration does not appear to be appropriate for performing this function. Yet for certain applications it is of importance to extract platelets separately, and for others to provide a platelet rich plasma.
There is therefore a widespread need for a closed system and method that will separate different constituents of whole blood that are differentiable in density and size, but only in a minor degree, and to be able to do so with a relatively low cost disposable unit that is closed to the exterior environment. A further aim is to provide a closed system and method for the separation of platelet rich plasma from whole blood.